Q.Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?

An oxide ore of copper can be reduced fairly directly ($Cu_2O + C \rightarrow 2Cu + CO$). Copper pyrites, however, first needs concentration by froth flotation, then partial roasting (removing sulphur as $SO_2$ and converting FeS to FeO), then smelting with silica to slag off the iron as $FeSiO_3$ (forming a copper matte of $Cu_2S$+FeS), and finally self-reduction in a converter to blister copper — a longer, multi-stage pyrometallurgical sequence because iron and sulphur must both be removed.

Step 1 – Composition of the two ore types

An oxide ore of copper (e.g. cuprite, $Cu_2O$) contains copper combined only with oxygen — reduction is comparatively simple, since carbon (coke) can directly reduce the oxide:

Copper pyrites ($CuFeS_2$), by contrast, is a mixed sulphide containing both copper AND iron, bonded as sulphides — extracting pure copper metal from it means both the sulphur and the iron have to be dealt with, not just the copper–sulphur bond.

Step 2 – The extra steps needed for pyrites

1. Concentration by froth flotation to remove gangue.
2. Roasting in excess air converts some sulphide to oxide and burns off part of the sulphur as $SO_2$:

3. Smelting the roasted ore with silica (as a flux) and coke in a reverberatory furnace: silica combines with FeO (from partial oxidation of FeS) to form a slag, $FeSiO_3$, that is skimmed off, leaving behind molten "copper matte" — a mixture of $Cu_2S$ and residual FeS.
4. Bessemerisation / converting: the matte is charged into a silica-lined converter and blasted with air; remaining FeS is oxidised and slagged off as $FeSiO_3$, and copper is finally obtained by self-reduction:

Step 3 – Why this makes it "more difficult"

Each of these steps (roasting, slagging, converting) is an additional pyrometallurgical stage not needed for a straightforward oxide ore, and controlling the removal of iron (without losing copper to the slag) and sulphur (as SO$_2$, requiring gas handling) adds real process complexity compared to a one-step carbon reduction of an oxide ore.

Compare the composition: an oxide ore reduces directly with carbon in one step, while a sulphide ore like copper pyrites also contains iron, requiring roasting + slagging (to remove Fe as $FeSiO_3$) + converter self-reduction before pure copper is obtained.

• Forgetting that copper pyrites contains IRON as well as copper — the extra difficulty is largely about removing iron, not just about sulphur.
• Omitting the silica-flux/slagging step, which is the key mechanism by which iron is actually removed.